Field of the Invention
This invention relates to a flexible magnetic disk cassette capable of being used for the recording and reproducing of various analog and digital signals, and a recording and/or reproducing apparatus for the flexible magnetic disk cassette. More particularly, this invention is concerned with a disk cassette having a cassette cover in which is rotatably accommodated a recording and reproducing disk having flexibility such as a sheet-like magnetic disk (magnetic sheet), and a recording and/or reproducing apparatus for the same.
Description of the Prior Art
Referring to FIG. 1, there is shown a conventional recording and reproducing disk cassette designated by the reference numeral 1, which comprises a flat cassette cover 4 in the form of a rectangular parallelepiped composed of upper and lower halves 2 and 3, and a sheet-like flexible magnetic disk (magnetic sheet) 5 accommodated rotatably within the cassette cover 4. The magnetic disk 5 has a magnetic layer formed on both surfaces thereof, and on the central part thereof there is a center core disk 6 consisting of a circular plate stuck thereon with adhesive or the like. In the central part of the center core disk 6 there is formed a rotary shaft insertion opening 7.
When the disk cassette 1 is installed (loaded) onto a magnetic recording and/or producing apparatus (not shown), a rotating carriage 8 engages in a center opening 3a of the lower half 3 and at the same time a rotary shaft 9 is inserted in the rotary shaft insertion opening 7. In this state the center core disk 6 is attracted and fixed onto the rotating carriage 9 by means of an attracting member (not shown) consisting of a magnet. In this case, the magnetic disk 5 is disposed centrally in its thickness direction in consideration of the construction and dimension of the cassette cover 4. On the other hand, the magnetic head 11 is inserted into a head insertion opening 10 formed in the lower half 3 and then is brought into contact with the magnetic surface of the magnetic disk 5.
In such a loaded state, the center core disk 6 is rotated together with the rotating carriage 9 by means of a driving unit such as a motor 12, whereupon the magnetic disk 5 is rotated within the disk cassette 1. In association therewith the magnetic head 11 is moved in a radial direction of the magnetic sheet 5 (namely in the direction of arrow in FIG. 27), thereby performing a desired recording or reproducing operation.
In the disk cassette 1 of this sort, in order to prevent the peripheral edge portion of the magnetic disk 5 from striking against and being bent by the upper and lower halves 2 and 3, a ring-like projection 13 is formed on the inner surface of the upper half 2 to restrict the displacement of the center core disk 6 relative to the cassette cover 4. The disk cassette is installed, for example, in the following dimensional relation relative to the cassette cover 4, the projection 13, the center core disk 6 and the magnetic disk 5. The thickness l.sub.1 of the cassette cover 4 is 3.4 mm; the plate thickness l.sub.2 of the upper half 2 is 0.8 mm; the plate thickness l.sub.3 of the center opening portion 3a of the lower half 3 is 1.3 mm; the projecting length l.sub.4 of the projection 13 is 0.5 mm; the spacing l.sub.5 between the magnetic disk 5 and the projection 13 and the spacing l.sub.5 between the magnetic disk 5 and a ring-like projection 14 of the lower half 3 are each 0.4 mm; the thickness l.sub.6 of the center core disk 6 is 0.5 mm; and the spacing l.sub.7 between the inner surface of the upper half 2 and the center core disk 6 is 0.4 mm (see FIG. 2). Thus, the magnetic disk 5 is disposed centrally in the thickness direction of the cassette cover 4.
However, when the disk cassette 1 is not installed on a magnetic recording and/or reproducing apparatus, that is when the disk cassette 1 is not in use, if the magnetic disk 5 and the center core disk 6 move toward the lower half 3 by virtue of their own weight as indicated with a dot-dash line in FIG. 2, there is formed a gap of about 0.3 mm between the tip end of the projection 13 of the upper half 2 and the upper surface of the center core disk 6. In the presence of this gap, the movement of the center core disk 6 is no longer restricted by the projection 13, that is the center core disk 6 and the magnetic disk 5 move freely in the horizontal direction within the cassette cover 4, so that the peripheral edge portion of the magnetic disk 5 may strike against the side of the cassette cover 4 and be bent thereby. Once the peripheral edge portion of the magnetic disk 5 is bent, it is no longer possible to perform a good recording and reproducing operation in the vicinity of the bent peripheral edge portion.
Such an inconvenience is overcome by making larger thickness l.sub.5 of the center core disk 6 and thereby making larger the overlapping length l.sub.8 between the projection 13 and the center core disk 6 at the time of installing of the disk cassette 1. But this has not been realized because of the resulting very narrowed space (particularly in the thickness direction) within the cassette cover 4 and because of, as previously noted, the requirement that the magnetic disk 5 must be disposed centrally in the thickness direction of the cassette cover 4.